With respect to specified designated buildings having a site area equal to or lager than 3000 [m2], such as commercial facilities and offices, the Act on Maintenance of Sanitation in Buildings, generally known as building sanitation administration law, stipulates a control standard value for air environment as 17 [degrees C.] to 28 [degrees C.] for indoor temperature, and 40 [%] to 70 [%] for relative humidity. The indoor temperature has come to be relatively easily controlled, thanks to the spread of air conditioners. However, the relative humidity is not sufficiently controlled yet and, in particular, the lack of humidification in winter seasons is a major issue.
Humidification methods for an indoor space thus far known include vaporization, steaming, and spraying. The vaporization is performed by blowing air through a water-absorptive filter for heat exchange between the moisture contained in the filter and the air current, so as to evaporate the moisture from the filter thus humidifying the indoor space. In the steaming method, a heating device that heats up water in a tank is turned on to evaporate the water, thereby humidifying the indoor space. In the case of spraying, water is pressurized so as to turn into fine droplets, and the fine droplets of water exchange heat with air current.
For example, Patent Literature 1 proposes a humidifier based on the known vaporization method, the humidifier including a multitude of plate-shaped water-containing members vertically erected parallel to each other with a predetermined ventilation path therebetween, and located between an upper chamber and a lower chamber. The water-containing members according to Patent Literature 1 each have the upper edge fitted in a slit formed on the bottom plate of the upper chamber and including small holes formed on the respective sides, and the lower edge held by a groove provided in the lower chamber. Patent Literature 1 also teaches that a porous metal, a sintered metal, gathered metal fibers, gathered ceramic fibers, or other types of porous material may be employed as the water-containing member.